Reaction injection molding (RIM) has become an important process for the manufacture of a wide variety of moldings. The RIM process is a process which involves the intimate mixing of a polyisocyanate component and an isocyanate-reactive component followed by the injection (generally under high pressure) of the mixture into a mold with subsequent rapid curing. U.S. Pat. No. 4,218,543 describes one particularly commercially significant RIM system, which requires the use of a specific type of aromatic amine as a crosslinker/chain extender. The preferred amine described in the '543 patent is diethyl toluene diamine (DETDA).
In the automotive industry, the application of RIM technology has been primarily to produce vertical parts (e.g. fenders and fascias) and has typically not been used in the production of horizontal body parts (e.g., trunks, hoods and roofs). In order to be useful for the production of horizontal body parts, the molded product 1) must have high stiffness, 2) must have a high quality surface, and 3) must be able to withstand the heat generated during further processing of the part (e.g., painting and curing the paint). Typically, such a part must have a flexural modulus of 750,000 psi or higher.
Fiber glass reinforcement of polyurethane RIM parts is known. See, e.g., U.S. Pat. Nos. 4,435,349, 4,792,576, and 4,871,789. When utilizing such fiber glass reinforcement, several problems are generally encountered, not the least of which is the production of a smooth surface (see, e.g., U.S. Pat. Nos. 4,610,835, 4,644,862, 4,781,876, 4,810,444, 4,952,358, 4,957,684, and 5,009,821).
Recently, a process was developed for preparing Class A surface, fiber-reinforced molded articles (U.S. Pat. No. 5,391,344 issued on Feb. 21, 1995, based on U.S. application Ser. No. 159,891, filed on Dec. 1, 1993 which is a Continuation-in-Part of U.S. patent application Ser. No. 07/798,479, filed on Nov. 26, 1991 now abandoned). The process broadly comprised injecting a specific formulation into a mold, allowing the formulation to fully react and removing the molded part from the mold. The formulation broadly required the use of a polymethylene poly(phenyl isocyanate) and a mixture of hydroxyl functional materials. While adequate for many applications, the formulation tended to blister after being subjected to further heat treatment at 150.degree. C. (which is typical for curing of the paint).
Hindered amines are known for a variety of use in the polyurethane art (see, e.g., U.S. Pat. Nos. 4,146,688, 4,595,742, 4,631,298 and 5,059,634).